Method of preparing alkaline earth metal salts of 1-leucovorin



Patented Aug. 31, 1954 METHOD OF PREPARING EARTH- METAL SALTS OF l-LEUCOVORINf Donna R. Cosulich, Plainfield, N. .L, assignor to American C'yanamid Company, New York,.N. 13.,

acorporation ofMa'ine NolDrawi'ng. Application June 28, 1952,. Serial No. 296,249

This invention relates to new organic compounds having increased biological activity. More particularly; it relates to-formyl-Z-5,6,7,8- tetrahydropteroyl-L(+) -glutamic acid and salts 4. Claims. (Cl. 260-2515) rated; This materialwas' recryta -ll-ize'd. from water fourtimes to constant rotation I This th 5 Its solubility in water is only about 2%.

In t past 5-formy}.5 6 7 8 tetrahydropteroy1 isomer is approximately twice as active for Leuglutamic acid has been described as ynthetic COTLOS'IfOC CitTO'UOTU/In as is the synthetic mixcitrovorum factor, folinic acid-SF, leucovorin, etc. tule (dZ-1e11C0V0Iin)- (Welch et al., Pharmacological Reviews 3, No. 4, The cationic a t of v0r an b pr 376-377 (1951)). It has been used clinically for 10 cipitatcd from substantially aq us s ution in controlling the toxicity of aminopterin and other which the concentration of s t s fr m 3% c antifclic acid compounds, and as a hematopoietic about The 0f the desired $31113, being drug The product as originally prepared ynmuch less soluble than the mixture, separates thetically had acomparatively low activity which out first and can be recovered by filtrationhas since been increased by treatment of the Should the p d OV0 itself be desynthetic product with alkali and other methods. sired, it can be Obtained y treating the Salt W t I have now found, however, that the synthetic a mineral acidproduct is a diasteareoisomeric mixture of the The following examples illustrate in deta l the and ZL f rm and t when t l-form is preparation of representative cationic salts of separated from the isomeric mixture it has an l-leucovolinactivity about twice as great as that of the mix- Example 1 ture. The biologically active ZL-isomer is desig- A mixture f 885 parts f the calcium Salt of mated 5-formyl-dl-5,6,'7,8-tetrahydropteroyl-L(+) -glu- The compound lcuccvorin has the fcllcwmg tamic acid (rotation about [a] =|14) in 885 Structural formula! parts by volume of water is warmed to 50 C. to

H dissolve. On cooling, 9.4 parts of calcium 5-forg i myl-l-5,6,7,8-tetrahydropteroyl-L(+) -glutamate O H 7 (rotation [ozIl about +2") is obtained. By furgQ 5 3N ther treatment of the mother liquor 12.4 parts 6 N 4 more of this product (rotation about +2) is isouoom-on-nfi 1 I OH By recrystallization of this material from water HO O I CH0 four times in 5-10% concentration pure calcium 5-formyl-l-5,6,7,8-tetrahydropteroyl -L(+) glu- Where the carbon atoms marked with an asterisk tamate with a constant rotation [a] =15.2 is are optically active. In separating a mixture obtained. The biological activity as measured of optical isomers into its components in the case against Leuconostoc citro'uorum is approximately of acidic substances the usual procedure is to predouble the unfractionated synthetic dZ-mixture. pare a salt with an optically active base, using The solubility of the uniractionated mixture in alkaloids such as brucine, strychnine, etc. and 40 water is approximately 30% to 40%, from which fractionally crystallizing. Since Solubility difiercalcium Z-leucovorin will separate. Its solubility ences are often obtained in this way. However, in in water is about 2%. preparing a pharmaceutical substance such highly Example 2 toxic materials are very undesirable as contamim 5 To 0.41 parts of 5-formyl-dl-5,6,7,8-tetrahydro- Surprisingly, it was found that the calcium or p y -g111tami0 acid in Parts O Water strontium salt of l-leucovorin was much less solis added sodium hydroxide to pH 7.5, 0.21 parts uble than the mixture of calcium or strontium of strontium chloride hexahydrate and parts dl-leucovorin. It is unusual that enough difby volume of ethanol. The precipitate is filtered, ference in solubility could be obtained by use of a 50 washed and dried to g 0-445 parts of strontium calcium or strontium salt in essentially aqueous 5-f0rmy1-dZ-5,6, y D 0l/ glumedium to allow separation. However, calcium tamate. This is reprecipitated by dissolving in dZ-leucovorin prepared in the usual manner was water and adding ethanol. Finally, the material soluble in water to the extent of 30-40%. On was dissolved in two parts of Water and cooled standing and cooling, calcium Z-leucovorin sepaseveral days. The crystalline salt is separated by decantation of the liquor and dissolved in 2 parts of water. The solution is treated with one part by volume of ethanol and cooled. After isolation, the precipitate weighs 0.16 parts of strontium 5-formyl-Z-5,6,'7,8-tetrahydropteroyl-L(+) glutamate,- which is more active for Leuco'nostoc citrovorum than the starting material.

I claim:

1. A method of preparing 5iormyl-Z-5,6,7,8- tetrahydropteroyl-L(+)-glutamic acid which comprises forming an alkaline earth metal salt of the group consisting of calcium and strontium salts of 5-formyl-dZ-5,6,'7,8-tetrahydropteroy1- L(+) -glutamic acid, allowingthe more insoluble 5-formyl-2-5,6,7,8-tetrahydropteroyl -L(+) glutamic acid cationic salt to precipitate, separating said precipitate, removing said alkaline earth metal salt radical and recovering said compound therefrom.

2. A method of resolving 5-formyl-dl-5,6,'7,8- tetrahydropteryl-L(+) -glutamic acid which comprises forming an alkaline earth metal salt of the group consisting of calcium and strontium 4 salts of the all compound, allowing the more insoluble 5-formyl Z 5,6,7,8 tetrahydropteroyl- L(+)g1utamic acid salt to precipitate, separating said precipitate and removing said alkaline earth metal salt radicals from the separated isomers.

3. A method of preparing calcium 5-formyl-l- 5,6,7,8-tetrahydropteroyl-L(+) -glutamate which comprises forming a calcium salt of 5-formyl-dl- 5,6,7,B-tetrahydropteroyl-L(-1-) -glutamic acid, allowing the more insoluble calcium 5-formy1-l- 5,6,7 ,8-tetrahydropteroyl-L(+) -glutamate to precipitate and recovering said product therefrom.

4. A method of preparing strontium fi-formyl- Z-5,6,7,8 tetrahydropteroyl L(+) glutamate which comprises forming a stronium salt of 5-formyl-dl-5,6,7,8-tetrahydropteroyl-L(+) -glutamic acid, allowing the more insoluble strontium 5-formyl-Z-5,6,7,8-tetrahydropteroyl -L(+) glutamate to precipitate and recovering said product therefrom.

No references cited. 

1. A METHOD OF PREPARING 5-FORMYL-L-5,6,7,8TETRAHYDROPTEROYL-L(+)-GLUATAMIC ACID WHICH COMPRISES FORMING AN ALKALINE EARTH METAL SALT OF THE GROUP CONSISTING OF CALIUM AND STRONTIUM SALTS OF 5-FORMYL-DL-5,6,7,8-TETRAHYDROPTEROYLL(+)-GLUTAMIC ACID, ALLOWING THE MORE INSOLUBLE 5-FORMYL-L-5,6,7,8-TETRAHYDROPTEROYL-L(+)- GLUTAMIC ACID CATIONIC SALT TO PRECIPITATE, SEPARATING SAID PRECIPITATE, REMOVING SAID ALKALINE EARTH METAL SALT RADICAL AND RECOVERING SAID COMPOUND THEREFROM. 